146 THE MORPHOLOGY OF THE COMMON CBAYFISH. 



joints ; and of two terminnl oval plates, which represent 

 the endopodite (en.p) and the exopodite (ex.p). The 

 latter is divided by a transverse suture into two pieces ; 

 and the edge of the larger or basal moiety is beset with 

 short spines, of which two, at the outer end of the series, 

 are larger than the rest. 



/ The second somite is longer than the first (fig. 1) ; it 

 has very broad pleura, while those of the first somite are 

 small and hidden by the overlapping front margins of the 

 pleura of the second somite. 



' In the female, the appendages of the second somite of 

 the abdomen are similar to those of the third, fourth, and 

 fifth somites ; but in those of the first somite (fig. S7, B), 

 there is a considerable variation. Sometimes, in fact, 

 the appendages of this somite are altogether wanting; 

 sometimes one is present, and not the other ; and' 

 sometimes both are found. But, when they exist, thesd 

 appendages are always small ; and the protopodite is 

 followed by only one imperfectly jointed filament, which 

 appears to represent the endopodite of the other ap-' 

 pendages. 



In the male, the appendages of the first and second 

 somites of the abdomen are not only of relatively larg^ 

 size, but they are widely difierent from the rest, those of 

 the first somite departing from the general type further 

 than those of the second. In the latter (C, C ') there is 

 a protopodite {cx.p, bp) with the ordinary structure, and' 

 it is followed bj' an endopodite (en.p) and an exopodite 



